Optical devices, such as laser diodes (LD) and light emitting diodes (LED) can be fabricated by crystal growth of a nitride-based group III-V compound semiconductor on a sapphire substrate, a SiC substrate, etc. As technical problems for optical devices of this type, there are improvements in heat dissipation performance and light extraction efficiency. It has been difficult for optical devices of this type to operate stably when a large current is flown therethrough.
Recently, a semiconductor light emitting device aiming for higher light extraction efficiency has been proposed, in which a III-V compound semiconductor formed on a sapphire substrate is mounted on a sub-mount substrate by flip-chip mounting, and then the compound semiconductor is fixed with an underfill material, and then the sapphire substrate is peeled off from the semiconductor, and then an upper surface of the compound semiconductor processed to make a rough surface.
However, when the underfill material is attached to the side faces of the sapphire substrate, an excess force is required to peel off the sapphire substrate by the laser lift-off method. It is thus concerned that the compound semiconductor may crack when the sapphire substrate is peeled off forcibly.
For this reason, there has been proposed a technique in which the underfill material is not attached to the side faces of the sapphire substrate (see Document 1: JP-A 2008-140873 (Kokai).)
However, in Document 1, although the underfill material is not attached to the side faces of the sapphire substrate, it is attached to the bottom surface of the sapphire substrate. Thus, an excess force is also required in order to peel off the sapphire substrate. This could cause a compound semiconductor and/or the underfill material to crack or break. Moreover, in order to form the underfill material having the shape disclosed in Document 1, further fabrication processes are required which leads to increase in fabrication cost.